Electrochemical machining (ECM) is a conventional process in which a workpiece is provided with a positive voltage to create an anode, and a pair of tools is provided with a negative voltage to create a cathode. DC voltages between about 5-25 volts and up to about 15,000 amps, or more, are typically used, and may be steady-state or pulsed. An electrolyte at pressures up to about 300 psi (21 kg/cm.sup.2) is channeled in the space or gap between the workpiece and the tools for electrochemically machining the workpiece.
The prior art includes various methods and apparatus for electrochemically machining airfoil blades, either individually on a single workpiece, or in multiples from a workpiece bar. Leading and trailing edges of an airfoil blade are especially difficult to electrochemically machine precisely, and the prior art teaches various apparatus therefor. Furthermore, with an airfoil blade having a transversely extending platform, the simultaneous electrochemical machining of both the airfoil and the platform is also especially difficult to accomplish, and the prior art teaches various apparatus therefor.
For example, the airfoil and platform may be electrochemically machined simultaneously by using cathode tools each having a feed axis inclined at an acute angle to the radial stacking axis of the blade, for example at about 60.degree. thereto. The included angle between the two, opposing, cathode tools is therefore about 120.degree.. During electrochemically machining, the two tools are moved toward the workpiece along the feed axes, and since the feed axes are inclined, the tools move both toward the airfoil of the blade and the platform of the blade for simultaneously electrochemically machining both.
The blade platforms may be disposed substantially perpendicularly to the blade stacking axis or may be inclined thereto. A gas turbine engine airfoil may be in the form of a rotor blade or a stationary stator vane, with the blade typically having a single platform at the root end thereof, with the vane typically having platforms at both the root and tips thereof.
Accordingly, in order to precisely electrochemically machine substantially the entire airfoil from leading edge to trailing edge, from root to tip, and along the platform or platforms, conventional ECM machines vary in degree of complexity and require the inclined feed axes for the simultaneous electrochemical machining of both the airfoil and the platform. However, with a stator vane having both root and tip platforms, electrochemical machining thereof must typically be accomplished in two steps in view of tool access limitations, firstly electrochemically machining a majority of the airfoil and one of the platforms, and then machining the remaining platform and airfoil adjacent thereto.
Typical prior art ECM machines include the cathode tools having inclined feed axes usually at only one angle of inclination. In order to change the angle of inclination of the feed axes for electrochemically machining either an individual airfoil in two steps, for example a stator vane having two platforms, or to machine variously configured airfoil blades, either different ECM machines having different inclination angles must be used, or an ECM machine must be physically reconfigured at the desired inclination angles. For example, the cathode tools, including their moving apparatus, may be reconfigured for varying their inclination axes. However such machines are relatively complex, and the reconfiguration process requires set up time and typically the use of hoists for lifting the heavy tool moving apparatus.
Furthermore, typical ECM machines are relatively complex and provide access to the workpiece from typically one side only. The remaining sides surrounding the workpiece typically include either actuation mechanisms or large frames for supporting the various components of the machine.
Yet further, typical ECM machines provide various, complex arrangements for sealing the electrolyte channeled over the workpiece for preventing undesirable leakage thereof or undesirable stray electrochemical machining of components adjacent to the workpiece, or both.